1. Field of the Invention
The present invention generally relates to fluid handling devices and methods for their use. More particularly, this invention relates to a fluid delivery system and an inline sensing unit capable of delivering controlled amounts of fluids.
2. Description of the Related Art
Infusion therapy generally involves the administration of a medication to a subject using intravenous (IV), subcutaneous and epidural routes. A wide variety of fluid infusion pumps have been developed over the years that are capable of delivering medication at a controlled rate. Such pumps include elastomeric, gravity fed, syringe, electrical and mechanical pumps. Valves and flow sensors have been incorporated into some infusion pump designs to improve dosage accuracy and to control the flow of fluids (e.g., drugs, medications, etc.) through these systems. More recently, micromachined flow sensors, valves and pumps have been developed, some of which have been used in medication and drug delivery applications. Precise fluid control and measurement made possible with the above equipment and devises can also be useful in other medical applications, such as drug compounding and urological and blood analysis.
Certain types of infusion therapies require extremely small amounts of fluids to be delivered in a very precise manner. In these situations, hand-actuated syringes are often not sufficiently accurate. Furthermore, hand-actuated syringes are prone to many types of human errors such as errors in dosage amount, dose rate, and medicine type. Machine-controlled pumps are capable of significantly better accuracy. For example, the accuracy of infusion pumps typically ranges from about +/−15% for volumetric pumps, down to about +/−3% for syringe pumps. Though Coriolis mass flow sensors can provide flow rate measuring accuracies of under +/−1%, their high cost and general requirements for relatively high flow rates have restricted their use in the medical field.
Commonly-assigned U.S. Pat. No. 6,477,901 to Tadigadapa et al. discloses a sensing device having a micromachined resonating tube that operates on the basis of the Coriolis effect to sense mass flow and density of a flowing fluid. The device can sense extremely low volumetric flow rates (e.g., less than 1 ml/hr) of the type required by drug delivery applications. The device uses an electrostatic drive and capacitive sensing, and therefore requires little power for its operation. Commonly-assigned and copending U.S. patent application Ser. No. 10/248,839 to Sparks utilizes the sensing device disclosed in Tadigadapa et al. in a fluid delivery system capable of delivering a precise amount of fluid and monitoring certain properties of the fluid so that the correct fluid is safely delivered to its intended destination. The fluid delivery system of Sparks is also equipped to measure elapsed time and to stop fluid flow in response to output signals of the sensing device. This micromachined sensor is ideal for obtaining the high accuracy, at low power levels and small size that is needed for drug infusion, compounding and medical analysis systems.
While Tadigadapa et al. and Sparks provide significant advancements for infusion systems and treatments, further improvements would be desirable.